1. Field of the Invention
The present invention relates generally to a method of manufacturing a hydrodynamic bearing, and, more particularly, to a method of manufacturing a hydrodynamic bearing in which a metal bearing, which is prepared by sintering metal powder, is internally subjected to chemical etching, such as done by an electrochemical machining process or an etching process, to form hydrodynamic pressure grooves thereon, thus assuring a high-precision and reliable hydrodynamic bearing.
2. Description of the Related Art
The hydrodynamic bearing, which is intended to rotatably support a rotating shaft that is rotated by externally applied electric current, holds a predetermined type of fluid between the rotating shaft and the bearing. In order to assure the smooth rotation of the rotating shaft, fine hydrodynamic pressure grooves, which perform a hydrodynamic pumping action of the fluid, are provided between either the rotating shaft or the hydrodynamic bearing.
An example of the methods of manufacturing such a hydrodynamic bearing is disclosed in Japanese Unexamined Patent Publication No. 2006-316896, which is schematically illustrated in FIGS. 9 and 10.
As shown in FIG. 9, the conventional method of manufacturing a hydrodynamic bearing is conducted in such a manner that metal powder M, which is a raw material of a shaft-supporting sleeve, is compressed between an upper punch 14 and a lower punch 13 which are forcedly moved toward each other, and the resulting compressed body Ma is sintered at a predetermined temperature, resulting in a sintered bearing body 15.
Subsequently, as shown in FIG. 10, in order to form hydrodynamic grooves on the internal surface of the sintered body 15, the sintered body 15 is put into a press die 16, and a core rod 17, having thereon protrusions corresponding to the desired hydrodynamic grooves, is inserted into the internal space of the sintered body 15. Thereafter, the external surface of the sintered body 15 is pressed using the press die 16, with the result that the internal surface of the sintered body 15 is formed with the hydrodynamic grooves.
The core rod 17 is separated from the sintered body 15, and then the sintered body 15 is separated from the press die 16, thus producing a desired shaft-supporting sleeve.
However, in the above conventional method of manufacturing a shaft-supporting sleeve, when the core rod 17 is separated from the sintered body 15, the hydrodynamic grooves of the sintered body may be damaged due to the protrusions of the external surface of the core rod 17, thus causing uneven hydrodynamic pressure to occur.
Furthermore, since the sintered body 15 must be made of metal powder having a spring back behavior, the raw material of the sintered body 15 is inevitably selected from restricted kinds of materials.
In addition, since the hydrodynamic grooves are formed by pressing the sintered body 15 after the compression and sintering processes of the metal powder M, the compressed structure of the sintered body 15 is not dense, thus deteriorating the durability of the sintered body 15.